An apparatus for monitoring the wear of the carbon brushes can be found, by way of example, in DE 197 58 235, DE 196 19 728 A1, and DE 196 19 733 A1. Various sensor systems for detection of the wear are provided in these documents.
Particularly in DE 196 19 733, optical sensors as well as inductive, capacitive or opto-electrical movement sensors are provided, via which the position and hence the wear of the carbon brush are intended to be detected. Furthermore, a piezoelectric sensor is provided as a force sensor for determining the spring force with which the carbon brush is pressed against the slip-ring. In addition, a fluid system is described, in which, beyond a certain carbon brush wear level, a flow path for compressed air is opened or closed.
All known systems require complex line routing, for example with electrical lines from the sensors to an evaluation and detection unit outside the plug-in brush holder or, by way of example, complex compressed air lines. When the carbon brushes are replaced, these lines must first of all be detached and must then be reconnected which, overall, leads to brush replacement being a time-consuming process. Particularly when the sensors are connected via electrical lines to an evaluation unit, additional measures are required for potential isolation and to withstand voltages.